Conventionally, a sintered body of cubic boron nitride has high hardness, and accordingly, it has been widely used as a material for tools such as cutting tools. Furthermore, it is also known to form a surface coating layer on a surface of a sintered body of cubic boron nitride for the purpose of improving wear resistance and the like.
For example, Japanese Patent Laying-Open No. 2005-047004 (Patent Literature 1) discloses a composite high-hardness material for a tool that is a sintered body of cubic boron nitride having a surface provided with an intermediate layer composed of a compound such as a nitride or a carbide of an element in group 4a, 5a, or 6a, and a coating such as TiAlN on the intermediate layer. Further, Japanese Patent Laying-Open No. 2002-144110 (Patent Literature 2) discloses a tool of a surface-coated sintered body of boron nitride that is formed of a sintered body of boron nitride having a surface provided with an intermediate layer composed of at least one element selected from group 4a, 5a, and 6a elements, and a hard coating layer on the intermediate layer. Furthermore, Japanese Patent Laying-Open No. 2000-129423 (Patent Literature 3) discloses a hard coating having a first layer composed of a metal in group 4a, 5a, or 6a formed on a substrate, and a second layer composed of TiAlVN or the like formed on the first layer.